1. Field of the Invention
The present invention relates to a skew adjustment mechanism for an optical pick-up used in an optical disc drive, and in particular relates to a tangential skew adjustment mechanism for an optical pick-up used in an optical disc drive.
2. Description of the Prior Art
Optical disc drives are apparatuses which emit a laser beam to a signal surface (recorded surface) of a recording medium such as a compact disc (CD) or a CD-ROM, and then reproduces (playing back) the recorded information which is recorded on the signal surface through a great number of pits formed spirally on the surface based on changes in light intensity of the reflected laser beam. Examples of such optical disc drives include a CD-ROM drive and a CD-R (recordable) drive and the like.
These optical disc drives are provided with an optical pick-up which emits a laser beam to the optical disc and receives the beam reflected therefrom. FIG. 23 is an exploded view which shows the structure of one of the conventional optical disc drives.
As shown in the drawing, the optical pick-up is generally composed of a pick-up base 110 which is guided in the radial direction of the optical disc by means of two guide rods 102, 104, an actuator base 120 which is held on the pick-up base 110, a damper base 130 which is mounted to the actuator base 120, a lens holder 150 which is supported displaceably in the focusing direction (F) and the tracking direction (Tr) through suspension springs 140, and an objective lens 160 provided in the lens holder 150.
In more details, the pick-up base 110 is formed from aluminum or other metal material using a diecasting process or the like. As shown in FIG. 23, the pick-up base 110 includes a laser diode (LD) 113 which emits a laser beam, a beam splitter 114 which reflects the beam fed from the laser diode 113, a mirror 115 which reflects the beam from the beam splitter 114 toward the objective lens 160 and a photodiode 116 which receives a reflected beam reflected on the signal surface of the optical disc through the objective lens 160, the mirror 115 and the beam splitter 114 and then generates electrical signals in response to changes in light intensity of the received laser beam. Further, the pick-up base 110 includes a pair of supporting surfaces 112 for supporting the actuator base 120 rockably about the virtual center axis (A) which extends in the radial direction of the optical disc in parallel with the guide rod.
The actuator base 120 includes a base frame 121 which is formed from a substantially square plate having a substantially square opening at the roughly central portion thereof. Therefore, the base frame 121 is comprised of a front plate portion 121a and a rear plate portion 121b which are spaced with each other along the longitudinal direction of the guide rod 102, and a right plate portion 121c which is positioned at the side of the guide rod 102 and a left plate portion 121d which is positioned at the side of the guide rod 104. On the outer edges of the front plate portion 121a and the rear plate portion 121b, there are integrally formed a pair of erected wall portions 122, 122, respectively, so as to direct upwardly. Each of these erected wall portions 122, 122 has receiving surfaces which are adapted to be in abutment with the supporting surfaces 112, 122 of the pickup base 110, respectively. Further, on the outer edge of the right plate portion 121c of the base frame 121, there is integrally formed a damper base supporting portion 124 so as to direct upwardly, and the damper base 130 is mounted to this supporting portion 124. Furthermore, on the inner and outer edges of the left plate portion 121d of the base frame, there are integrally formed yokes 126, 127, respectively, so as to direct upwardly. On the inner surface of the inner yoke 126, there is provided a magnet 128.
As stated in the above, on the damper base supporting portion 124 of the actuator base 120, the damper base 130 is mounted through a screw 132. From the upper and lower portions of both sides of the damper base 130, four suspension springs 140 extend toward the lens holder 150 to support the lens holder 150 so as to be displaceable in both the tracking direction and the focusing direction.
On the lens holder 150, there are provided a focusing servo coil 152 and a tracking servo coil 154. These coils are arranged such that the yoke 126 of the actuator base 120 is positioned within the tracking servo coil 152 and the yoke 127 is positioned so as to face the focusing servo coil 154, respectively, when the damper base 130 is mounted to the supporting plate portion 124 of the actuator base 120.
In the optical pick-up having the above structure, the beam emitted from the laser diode 113 is reflected by the beam splitter 114 toward the mirror 115, and the beam reflected on the mirror 115 is focused onto the signal surface of the optical disc through the objective lens 160. The beam reflected on the signal surface of the optical disc passes the objective lens 160 and the beam is then reflected on the mirror 115 again and passes through the beam splitter 114, and then the beam is received by the photodiode 116. In this way, electrical signals responsive to changes in the light intensity of the received beam are produced in the photodiode 116, and based on thus produced electrical signals, the information recorded on the signal surface of the optical disc are reproduced.
In order to accurately read out the information recorded on the signal surface of the optical disc using the optical pick-up 100 having the above described structure, it is required that an optical axis of the beam emitted toward the optical disc through the objective lens 160 is directed vertically with respect to the signal surface of the optical disc such that the beam is properly focused on the signal surface.
However, the optical pick-up is composed of a plurality of components or parts as described above, so that there is a case that the beam is not always emitted to the signal surface of the optical disc vertically because of dimensional deviations of the respective components or parts and deviations caused upon assembling.
For this reason, the optical pick-up is provided with a skew adjustment mechanism for adjusting the direction of the beam when assembling the components and parts. In general, the skew adjustment is carried out through a radial skew adjustment and a tangential skew adjustment.
The radial skew adjustment means to adjust the beam emitting direction along the radial direction of the optical disc. In the prior art optical pick-up, such a radial skew adjustment is carried out by appropriately rotating the damper base 130 about the screw 132 in the directions indicated by the arrow (R) in the drawing.
For this purpose, in this prior art optical pick-up, a screw hole 135 is formed on the lower surface of the damper base 130 at one side thereof, and a screw 137 which passes the base frame 121 of the actuator base 120 is threaded thereinto, as shown in FIG. 24. Further, on the other side of the lower surface of the damper base 130 which is opposite to the screw hole 135, a concave portion 136 is formed and a spring 138 is disposed between the bottom of the concave portion and the actuator base 120. This spring 136 urges the damper base 130 so that the damper base can rotate about the screw 132 in the anti-clockwise direction.
When the radial skew adjustment is to be carried out, first the screw 132 is loosened so that the damper base 130 can be pivoted about the axis of the screw 132. Then, the screw 137 is adjusted from the underside of the actuator base 120 to rotate the damper base 130 to a desired position, and in this state the screw 132 is fastened to fix the damper base 130 onto the supporting plate portion 124 at that position. In this way, the lens holder 150 is also rotated with respect to the axis of the screw 132 so that the beam emitting direction from the objective lens 160 can be adjusted in the radial direction of the optical disc as shown by the arrow (R) in FIG. 23.
On the other hand, the tangential skew adjustment means to adjust the beam emitting direction along the tangential direction normal to the radial direction of the optical disc. In the prior art optical pick-up, such a tangential skew adjustment is carried out by displacing the mounting position of the actuator base 120 with respect to the pick-up base 110 in the direction shown by the arrow (Ta) in FIG. 23.
For this purpose, in this prior art optical pick-up, a screw 125 which passes the pick-up base 110 is threaded into one side of the actuator base 120 from the underside of the pick-up base 110 as illustrated in FIG. 25 in a simplified manner. Further, a spring seat member 129 is provided at the other side of the actuator base 120 opposite to the screw 125 with respect to the supporting surface 112 of the pick-up base 110. The spring seat member 129 is a rod-shaped member, and it passes through the pick-up base 110 and is anchored with the other side of the actuator base 120. At the lower end portion of the spring seat member 129, there is formed a spring seat. A spring 129a is disposed between the bottom surface of the pick-up base 110 and the spring seat to urge the actuator base 120 by the biasing force of the spring so that the actuator base 120 rotates in the anti-clockwise direction in the drawing.
In this prior art optical pick-up, the tangential skew adjustment is carried out by adjusting the screw 125 appropriately from the underside of the pick-up base 110 to rotate the actuator base 120 about the virtual axis A described above, thereby adjusting the beam emitting direction in the tangential direction.
As described above, in the prior art optical pick-up, both the radial skew adjustment and the tangential skew adjustment are carried out by adjusting the screws 132, 125 from the underside of the actuator base 120 and the pick-up base 110. Therefore, in this prior art optical pick-up, it is not possible to make such skew adjustments after the optical pick-up has been assembled with the optical disc drive.
However, even if such skew adjustments have been carried out before the optical pick-up 100 is assembled with the optical disc drive, there still remain a case that the optical axis of the beam is not directed to the signal surface of the optical disc vertically after the optical pick-up is assembled with the optical disc drive because of mounting state of the guide rod or preciseness of the resin molding parts or the like. If such a case would occur, a jitter characteristic of the optical pick-up 100 is lowered.
Therefore, it is desired that skew adjustments can be carried out even after the optical pick-up is assembled with the optical disc drive. In particular, in the case of CD-R drive in which data is writable to an optical disc, a deviation of the optical axis of the laser beam affects a writing performance even though it is very small, and therefore more precise skew adjustment is required. Therefore, it is desirable that skew adjustments could be also carried out even after the optical pick-up has been assembled with the optical disc drive.
The present invention has been made in view of the problem involved in the prior art optical pick-up. Accordingly, it is an object of the present invention is to provide a skew adjustment mechanism for an optical pick-up used in an optical disc drive in which a tangential skew adjustment can be carried out easily even after the optical pick-up is assembled with the optical disc drive.
In order to achieve the object, the present invention is directed to a skew adjustment mechanism for an optical pick-up used in an optical disc drive, the optical pick-up being provided in the disc drive freely movable in a radial direction of an optical disc along a guide rod for playing back or recording and playing back the optical disc, wherein the skew adjustment mechanism comprises a tangential skew adjustment mechanism for adjusting tangential skew of the optical pick-up after the optical pick-up has been assembled into the disc drive.
In this skew adjustment mechanism, the optical pick-up includes a pick-up base having a first end and a second end opposite to the first end, the first end being slidably connected to the guide rod, and the tangential skew adjustment mechanism includes a displacement means provided on the second end of the pick-up base for rotationally displacing the pick-up base about an axis of the guide rod.
The displacement means is preferably composed of a screw which vertically passes through the second end of the pick-up base such that a lower end portion of the screw protrudes from the bottom surface of the pick-up base and a sliding surface positioned a prescribed distance below the bottom surface of the second end of the pick-up base so that the lower end portion of the screw is in contact with the sliding surface, whereby the pick-up base can be displaced by adjusting the protruding length of the lower end portion of the screw.
According to the tangential skew adjustment mechanism having the structure described above, it is still possible to adjust tangential skew even after the optical pick-up 30 has been assembled into the optical disc drive, since the optical pick-up can be rotationally displaced with respect to an axis of the guide rod by appropriately adjusting the screw from the upper side of the optical pick-up.
The tangential skew adjustment mechanism may further include a biasing means for biasing the pick-up base in a direction which causes the lower end portion of the screw to abut the sliding surface.
In this case, it is preferred that the biasing means is constructed from a plate spring provided on the second end of the pick-up base and a downward facing abutment surface provided a prescribed distance above the sliding surface, in which the plate spring is adapted to slidably abut onto the downward facing abutment surface to produce a biasing force for rotating the pick-up base downwardly about the axis of the guide rod.
Another aspect of the present invention is directed to a skew adjustment mechanism for an optical pick-up used in an optical disc drive, the optical pick-up being provided in the disc drive freely movable in a radial direction of an optical disc along a guide rod for playing back or recording and playing back the optical disc, and the optical pick-up including a pick-up base having a first end which is slidably connected to the guide rod and a second end opposite to the first end, wherein the skew adjustment mechanism comprises a tangential skew adjustment mechanism for carrying out tangential skew adjustment by rotationally displacing the pick-up base with respect to an axis of the guide rod.
In this arrangement, it is preferred that the second end of the pick-up base includes a bottom surface, in which the tangential skew adjusting means includes a screw which vertically passes through the second end of the pick-up base such that a lower end portion of the screw protrudes from the bottom surface of the pick-up base and a sliding surface positioned a prescribed distance below the bottom surface of the second end of the pick-up base so that the lower end portion of the screw is in contact with the sliding surface, whereby the pick-up base can be displaced by adjusting the protruding length of the lower end portion of the screw.
The other aspect of the present invention is directed to a skew adjustment mechanism for an optical pick-up used in an optical disc drive, in which the optical pick-up comprises a pick-up base movable in a radial direction of an optical disc along a guide rod provided on a chassis of the disc drive, an actuator base held on the pick-up base so as to be pivotal with respect to a virtual axis that is parallel to the guide rod, and a lens holder which is supported by the actuator base so as to be displaceable at least in tracking direction and focusing direction and which has an objective lens, wherein the skew adjustment mechanism comprising a first tangential skew adjustment mechanism for rotationally displacing the actuator base relative to the pick-up base about the virtual axis; and a second tangential skew adjustment mechanism for rotationally displacing the pick-up base about an axis of the guide rod.
According to the skew adjustment mechanism having the above described structure, not only it is still possible to adjust tangential skew even after the optical pick-up 30 has been assembled into the optical disc drive, but also it becomes possible to carry out a more precise tangential skew adjustment, since different two types of tangential skew adjustments can be made by the provision of the first and second tangential skew adjustments.
Other objects, structures and advantages of the present invention will be apparent when the following description of the preferred embodiments is considered taken in conjunction with the accompanying drawings.